Tire Size Recommendations

My BMW is a 2007 328I Coupe. Car needs new tires and has OEM 17 x 8 wheels (224/45 17 Tires). I would like to go with a larger tire, possibly staggered...What’s the largest size(s) tires can I put on these wheels?

A quick perusal of the specs of a couple of tires in the next couple sizes up (235/40-17 & 245/40-17) on tirerack.com for those two sizes shows a recommended wheel-width range starting @ 8", so presumably you could mount either of those two sizes on your stock rims without having the sidewalls unsafely ballooned. Checking a couple of 255/40-17 specs shows a starting minimum recommended width of 8.5, so it looks like 245's would be the max width you're going to safely get on your stock rims & anything wider should be on wider rims. You'll have some speedo difference w/ 245/40 or 235/40. Considering most BMW's the speedo reads about 4-5mph high anyway, I never worry much about speedo differences from having a changed rolling diameter, I just try to understand what the difference is so I can have an idea what my actual speed is. You don't want a larger rolling diameter, so a 45 aspect ratio for the two wider sizes I don't think would be recommended. Personally I'm not a fan of staggered setups and prefer the more balanced handling of a square setup, plus the advantage of being able to rotate the tires front-to-back & vice-versa which allows for evening-out the neg. camber wear on the rears when they're swapped to the zero-neg.-camber front end (stock alignment camber). BMW puts staggered setups on the cars to make them inherently understeer, which can be safer for the average driver; a square setup helps dial out the understeer, increasing the potential for oversteer.

You can use this to compare stock vs. other sizes to help assess approximate fit -

You can look up original rims on realoem.com, either use the last 7 of your vin or correct production month & year. Picking a random-month for an '07 328i coupe, it looked like o.e. 17x8's were et 34 (ie, 34mm offset).

It probably would be worthwhile to chat w/ a Tire Rack sales rep on tire choice and fitment advice.